1. Field of the Invention
The invention relates to a closure device for bottles comprising a screwable cap.
It relates more particularly to such a device comprising a plastic material cap with a pilfer or tamper proof strip integral with said cap as long as the bottle has not been opened a first time.
2. Description of the Prior Art
Numerous devices of this type are already known which find applications more particularly for closing bottles containing drinks such as aerated or mineral waters.
The simple constructions of known devices, in which a cylindrical thread of the cap cooperates with a mating thread on the neck of the bottle are not always satisfactory in so far as their sealing is concerned, whereas more complex constructions are difficult and expensive to manufacture. In known devices, the sealing depends not only on the relative hardness of the materials forming the bottle and the cap, but also on the degree of mechanical accuracy of the parts which cooperate together, as well as on the more or less good quality of screwing during the bottling operation.
Now, because of their methods of manufacture, plastic material bottles obtained by extrusion/blowing of PVC frequently have imperfections of shape as regards their neck and as regards their neck end face, which is not always rigorously flat due to the cut of the plastics tube resorted to to manufacture the bottle. Moreover, and for bottles of this type with a rectangular cross section, different elongations of the neck and of the non cylindrical part adjacent thereto sometimes give rise to deformations of the neck and to oval shaped parts therein, which result in unsatisfactory stoppering of the bottles particularly when modern bottling machines are used whose capacity is of the order of 30,000 bottles per hour. The consequences then are deterioration of the contents of the bottle or else, for bottles containing fizzy drinks, risks of seeing the cap expelled during bottling or during transport and storage at a selling point.
In order to solve this problem, attempts have been made using insert type caps with conical thread means adapted to cooperate with matching thread means of the bottle.
Such a cap is shown, for instance, in DE-A-2 323 561. In the cap there described, however, sealing is obtained through cooperation of an edge of the container with a groove of the cap. Accordingly, such a device cannot be used for bottles which might show slight differences in shape, such as PVC extrusion/blown bottles. In addition, the cap described in the prior art publication has an angle of about 30.degree. so that the cap is thick and thus costly.